Optimizing Machining and Workholding for Metal Additive Manufacturing

Additive Manufacturing (AM), also known as 3D printing, has garnered attention as a production technology for highly customizable products across a wide range of materials imaginable. Thanks to its design flexibility, 3D-printed metal parts can be manufactured for applications ranging from aerospace to medical. However, the unique designs of AM pose a challenge. Newly printed metal parts require additional machining steps to remove support structures, while the rough surface finish and unreliable dimensional accuracy of some deposition processes can hinder precise features like mating surfaces and threaded holes. Because complexity is unnecessary for the additive manufacturing process and parts need not conform to typically orthogonal shapes, customized parts may also have shapes that make machining particularly difficult. This article will examine how manufacturers today can overcome some of these challenges and optimize their AM processes.

Why Use Metals for Additive Manufacturing?

AM is an ideal process for metals because it allows for the fabrication of metal parts without traditional tooling, bypassing many geometric constraints and enabling the consolidation of parts for more efficient designs. This makes some metal alloys ideal materials for aerospace, automotive, and medical applications, as well as improving productivity in injection molding processes and expanding capabilities in creative industries like architecture.

Metals particularly suited to welding and casting are ideal for 3D printing. Conversely, metals that are difficult to machine or costly in terms of machining are also ideal for AM. Some of the most commonly used metals include titanium, aluminum, stainless steel, tool steel, Inconel, copper, and tungsten. Titanium is popular in aerospace and medical applications due to its lightweight. With an internal lattice structure, implantable grafts can be designed to accommodate bone growth. On the other hand, steel can be used to print sturdy parts capable of withstanding harsh environments, such as combustion processes or high-pressure containment. These metals and others can be printed from either powder or melt wire. Metal AM can be performed using several techniques including Selective Laser Melting (SLM) for powder bed, Laser Metal Deposition (LMD) for powder or wire, and Wire Directed Energy Deposition (WDED).

SLM is popular for producing smaller, more complex parts by using a "building" technique, selectively melting metal powder using a CO2 laser beam along the X and Y axes, layer by layer on a gradually lowering bed in an inert gas environment. A roller flattens the bed as the tray descends before the next laser beam exposure.

WDED uses a laser beam to melt wire fed through a nozzle, typically in a sealed gas enclosure. This method achieves higher deposition rates than SLM but may have lower resolution. WDED is popular in applications requiring simpler parts and where traditional manufacturing techniques are slow or expensive, such as in aerospace and automotive.

With such techniques, AM can significantly save costs and time for difficult-to-produce parts while allowing for the creation of smaller, more complex parts. However, AM has its drawbacks.

Additional Machining Steps Often Needed for 3D Printed Metal

Frankly speaking, 3D-printed metal parts are often not the solution for a manufacturer looking to produce parts in high-volume production. AM is ideal for smaller batch products, emphasizing customization and unique design over absolute quantity. Unfortunately, even high degrees of design flexibility present their own issues.

Metal parts printed from machines come out not smooth and are often manufactured in unique shapes, necessitating support structures to help the part stand upright and stable during printing. Therefore, additional machining steps are necessary to remove support structures and perform surface finishing.

Parts with unique shapes pose more challenges when Precision Mechanical Machining. During finishing, a part may need to be held at different angles, requiring the manufacturer to understand how the machining part will relate to the cutting tool and how it will contact the machining center table.